Complex object consisting of multiple partly overlapping shapes, blend together to keep one outer shell
I found out, that applying a union boolean on an exact copy in the exact same location actually does what i'm looking for... but it wouldn't do it on the hair i had (i used screw and solidify). So, i went back to the original file, i removed all children particles, converted the particles to mesh, and then selected all, and extruded them for width, and selected all again, to extrude them for depth. After joining this mesh with the body and head, i COULD make a duplicate and perform the boolean union on the entire object. 

For now, the solution will have to do. But i still can't understand there is no simpler way to do this. Mindboggling actually.